PTEN and TNF-α regulation of the intestinal-specific Cdx-2 homeobox gene through a PI3K, PKB/Akt, and NF-κB-dependent pathway

Background & Aims: PTEN (phosphatase and tensin homologue deleted from chromosome 10) is a dual-specificity phosphatase implicated in embryonic development, intestinal cell proliferation and differentiation, and tumor suppression. The transcription factor Cdx-2 is critical in intestinal development and homeostasis, and its expression is altered in colorectal cancers. However, the regulation of the Cdx-2 gene has not been entirely elucidated. Here, we hypothesize that Cdx-2 may be a target of PTEN signaling in the intestine. Methods: The expression patterns for Cdx-2 and PTEN along wild-type mouse colon, as well as in colon tumors occurring in Pten^+/- mice, were examined. The effect of PTEN or phosphatidylinositol 3-kinase inhibition and tumor necrosis factor α on Cdx-2 messenger RNA and protein expression, Cdx-2 DNA binding activity, and the promoter activity of the Cdx-2 gene was analyzed in human colon cancer cell lines. Results: Cdx-2 expression correlates with PTEN along the length of the murine colon and in colonic polyps that develop in Pten^+/- mice. In colon cancer cells, PTEN stimulates Cdx-2 protein expression and the transcriptional activity of the Cdx-2 promoter. Phosphatidylinositol 3-kinase inhibition by wortmannin or by a dominant-negative phosphatidylinositol 3-kinase mimics the Cdx-2 stimulation by PTEN. Inversely, cell treatment by tumor necrosis factor α decreases Cdx-2 expression. Phosphatidylinositol 3-kinase inhibition by PTEN or wortmannin has an inverse effect compared with tumor necrosis factor α on the balance between the p50 and p65 subunits of nuclear factor κB. p65 inhibits the activity of the Cdx-2 promoter, whereas p50 prevents p65 action. Conclusions: Our results suggest that the intestinal Cdx-2 homeobox gene is a target of PTEN/phosphatidylinositol 3-kinase signaling and tumor necrosis factor α signaling via nuclear factor κB-dependent pathways.